Peristaltic pumps generally comprise a housing member defining an arcuate surface less than 360.degree. and receive a resilient tubing in the inner radial periphery of the housing. A rotatable member having pressure elements or rollers engages the resilient tubing at spaced apart points and compresses the tubing. As the pressure elements move along the tubing, a liquid is drawn from a suction end and supplied under pressure to a supply end.
Peristaltic pumps are widely used; however, they inherently contain three main drawbacks. By virtue of the construction, a relatively high torque is required to drive the rotating member, the resilient tubing is subject to stretch or creep due to the pressure exerted thereon in an attempt to achieve complete closure of the tube, and there is always some backflow as the pressure point leaves engagement with the tubing near the discharge end. The high pressure exerted on the tubing further contributes to the required driving torque.
Peristaltic pumps have generally been constructed with a flexible, annular cross-section tube or pipe, which is disposed radially inwardly of a backing member. A rotatable member having a plurality of pressure rollers or cams compresses the tubing against the backing member and draws and pumps a fluid from a suction port to a discharge port. When such an annular cross-section tube is compressed to flattening, the radially inner and outer sides are flattened against each other, but the resulting bends at the sides of the flattened tube leave small residual gaps or clearances. This is detrimental because the resulting gaps detract from the pump's efficiency, do not provide positive liquid displacement, and the high strains created in the sides of the tube increase torque and aggravate the stretch or creep problem of the tube. U.S. Pat. No. 2,693,766 attempts to solve this problem with tubing especially moulded to have walls of decreased thickness at diametrically opposite areas, and specially formed backing members. However, this construction does not alleviate the problem of the high torque required to compress the tubing against the backing member.
Other embodiments of peristaltic pumps are shown in U.S. Pat. Nos. 2,885,967; 2,899,906; 2,930,326; 2,955,543; 2,977,890; and 3,358,609.
The present invention provides a peristaltic pump of new and improved construction which substantially reduces the required driving torque, provides a tube configuration which essentially eliminates tube stress leading to stretch or creep, and eliminates backflow from the supply.